| Mixing layer height(MLH) is one of the main factors affecting the atmospheric diffusion, the study of the atmospheric mixing layer plays an important role in atmospheric environmental quality assessment and total amount control. Based on ceilometers (Vaisala company, model CL51, CL31) data, This paper observed mixing layer height in Beijing-Tianjin-Hebei region four sites (Beijing, Tianjin, Shijiazhuang, Qinhuangdao) form October.16th 2013 to October.15th 2014 and analyzed its change characteristics.Results show that annual average of MLH in Beijing, the highest for 688±250m; Tianjin times, for 597±219m, and MLH in Qinhuangdao and Shijiazhuang is low, values are 444±180m and 547±257m respectively; But the seasonal variation characteristics are different:from high to low arrangement according to MLH is in turn Beijing, Tianjin, Shijiazhuang, Qinhuangdao in spring, values are 816,637,606,448 respectively; In the summer, in turn, is Beijing, Shijiazhuang, Tianjin, Qinhuangdao, value 832,748,681 and 748 respectively; In the autumn, in turn, is Beijing, Tianjin, Shijiazhuang, Qinhuangdao, value 556,555,510 and 555 respectively; in the winter, in turn, is Beijing, Tianjin, Qinhuangdao, Shijiazhuang, value 555,519,492 and 519 respectively, local temperature change is the main reason of change position of MLH in Shijiazhuang. The surface high concentrations of pollution may have a negative feedback effect on MLH; In Beijing, Tianjin and Shijiazhuang,from spring to summer each station of the increase of MLH is different, from autumn to winter, each station of the decrease of MLH is different and the winter average s in each site are the lowest of the year, MLH in Qinhuangdao summer significantly lower,381±133 m, the other seasons MLH maintained at 465+205 m. Statistics daily variation of MLH in all city present high during the day, night low form of unimodal type variation characteristics, diurnal variations change significantly, In the summer, statistics hourly average of MLH in Qinhuangdao is lower than other three sites, Diurnal variation is the lowest; Variation characteristics of mixed layer in 4 city have their own typical local characteristics.Combined with the meteorological data, we found that mixed layer in Beijing, Tianjin and Shijiazhuang obviously affected by the influence of thermal buoyancy lift during the day, mixing layer in Qinhuangdao and Tianjin is enhanced by wind at night, and because of low wind speed in Beijing and Shijiazhuang, turbulence effect is not obvious. The change of temperature play an important role on MLH seasonal variation in Tianjin, Beijing and Shijiazhuang area. And the change of prevailing winds play an important role on MLH seasonal changes in Qinhuangdao area.Combined with the PM2.5 data, we found that in all sites the atmospheric concentration of fine particulate matter increased as the MLH decreased, but there is a significant difference among sites, the opposite change tendency is more obvious in Shijiazhuang and Tianjin while in Beijing and Qinhuangdao is not obvious.This article will mass concentration multiplied by mixing layer height on behalf of the four urban atmospheric fine particulate matter pollution load (PM2.5 x MLH). Results show that in spring and summer sites in Shijiazhuang, Beijing and Tianjin, mobile emission source contributions to their respective region is larger, but in the autumn and winter, Beijing affected by motor vehicle emission source (car) relatively less during the day and still significantly affected by diesel vehicles in the night; Unfavorable atmospheric diffusion conditions are the main causes of the high concentration pollution in Shijiazhuang for a long time, especially elevated source contributed significantly to PM2.5; Although PM2.5 pollution in Tianjin reached high values in rush hour in the morning and at night, In the middle of the atmospheric pollution load reaches the maximum, suggests that air pollution is affected by motor vehicles and coal. Due to the sea-land breeze cleaning effect, Qinhuangdao annual atmospheric pollution load is low. All the year round the whole pollution load in Qinhuangdao is low, unable to effectively identify local contribution to PM2.5 pollution emissions.MLH in Beijing, Tianjin, Shijiazhuang and Qinhuangdao are presented high during the day, low in the night in common, but seasonal change in each city has its own characteristics. Elements affecting atmospheric pollution load in each city have significant difference. MLH changes Characteristics of meteorological elements are not all the same. Shijiazhuang in the winter affected by elevated point sources, Beijing affected significantly by diesel night, Tianjin influenced by motor vehicles and coal dual, Qinhuangdao is difficult to use the research methods. The results of the study is of great significance for cognitive Beijing-Tianjin-Hebei area pollution distribution, and can provide a scientific reference for reasonable distribution of regional pollution sources. |
PDF Full Text Request